Designable features of metal-organic frameworks for diverse gas separation membranes

1 Introduction

Gas separation is a critical unit operation in the chemical and energy industries, with broad relevance to H₂ purification, natural gas sweetening, CO₂ separation, air separation, and hydrocarbon separations (Favre, 2026; Baker, 2002). Because many of these processes are highly energy intensive, membrane-based separation has received increasing attention as an attractive alternative to conventional technologies such as distillation, pressure swing adsorption (PSA), and temperature swing adsorption (TSA), owing to its lower energy consumption, smaller carbon footprint, and simpler operation (Gao et al., 2024; Bernardo et al., 2009). However, the performance of conventional polymer membranes is still limited by the intrinsic permeability-selectivity trade-off, as well as issues related to physical aging and plasticization under realistic operating conditions (Ding, 2020; Gorgojo et al., 2014; Shin et al., 2020).

In this context, metal-organic frameworks (MOFs) have emerged as a promising class of membrane materials because of their exceptionally high surface area, tunable pore sizes, adjustable organic functionality, architectural flexibility, and thermal and physical stability (Howarth et al., 2016; Qian et al., 2020; Kang et al., 2017). The modular combination of metal nodes and organic linkers enables precise control over both pore structure and chemical environment, making MOFs attractive not only as pure crystalline films but also as fillers in mixed-matrix membranes (MMMs) (Yu et al., 2024; Venna et al., 2015; Arjmandi and Pakizeh, 2014). In particular, the designability of MOFs offers opportunities to regulate molecular sieving, adsorption selectivity, and interfacial compatibility in a way that is difficult to achieve with traditional porous materials (Ashtiani et al., 2026; Wang et al., 2016; Bi et al., 2020; Hardian et al., 2024).

Despite these advantages, practical implementation of MOF-based membranes still faces several challenges, including scale-up fabrication, membrane substrate adhesion, defect formation during growth or activation, and stability under humidity, pressure, and gas impurities (Kang and Lee, 2023; Li et al., 2023). For MMMs, poor filler dispersion and interfacial incompatibility can limit the achievable particle loading and reduce separation performance, whereas pure MOF films often suffer from grain-boundary defects and mechanical fragility (Seoane et al., 2015; Tanh Jeazet et al., 2012; Wang et al., 2015; Hasan and Coronas, 2024). Accordingly, current research is increasingly focused on strategies such as 2D nanosheet fabrication, pore size tuning, functional group engineering, and hybridization with complementary materials to improve both performance and stability (Yu et al., 2024; Peng et al., 2017; Shu et al., 2020; Li et al., 2026).

In this review, we summarize the designable features of MOFs and their application in gas separation membranes. While several comprehensive reviews have summarized the broad progress of MOF-based membranes, this mini review provides a distinct, target-oriented perspective. Rather than presenting a general overview of recent developments, it focuses on how the designable characteristics of MOFs can be tailored to address the transport requirements and material challenges associated with representative gas separations, including H₂, CO₂, olefin/paraffin, and O₂/N₂. By linking structural design strategies with the transport behavior of target gas systems, this review provides insights into the fundamental mechanisms governing selective molecular transport across various membrane architectures. First, the tunability of pore size, functional group engineering, and hybrid membrane design are discussed as key strategies for optimizing separation performance (Luo et al., 2025; Lin et al., 2021; Ahmadian-Alam and Mahdavi, 2021; Liu et al., 2017). An overview of these design strategies and their relationship to representative gas separation applications is schematically illustrated in Figure 1. Then, representative examples of MOF-based membranes for hydrogen separation, carbon dioxide separation, and other challenging gas separations are reviewed, with emphasis on the relationship between structure, interface, and transport behavior (Abdul Hamid et al., 2021; Ockwig and Nenoff, 2007; Ercan et al., 2021; Hou et al., 2019; Xu et al., 2020; Ashtiani et al., 2021).

2 Designable features of MOFs for gas separation

MOFs are crystalline nanoporous materials distinguished by their high accessible surface area, tunable pore sizes, adjustable organic functionality, architectural flexibility, and thermal and physical stability (Su et al., 2025). These features make MOFs highly attractive for membrane-based gas separations, setting them apart from conventional porous materials such as zeolites and activated carbon (Li et al., 2012). In particular, the modular combination of metal nodes and organic linkers enables precise control over both the structure and chemistry of MOFs, allowing them to be widely applied not only as pure MOF films but also as fillers in MMMs. Recent studies have increasingly focused on ultrathin 2D nanosheets, pore size fine-tuning, and integration with other species as key strategies for improving MOF membrane performance. Representative examples illustrating these design strategies are presented in Figure 2 and discussed in the following sections.

2.1 Fine-tuning of pore size

One of the most notable advantages of MOFs is their highly tunable pore size and pore aperture. This can be achieved through various approaches, including linker length variation, ligand composition, metal center selection, framework flexibility, defect engineering, and post-synthetic treatment (Zhu et al., 2021; Choi et al., 2024). For instance, mixed-linker strategies and metal substitution can adjust the effective pore aperture and thereby alter molecular sieving behavior, while guest inclusion or post-functionalization can further narrow pore openings or modulate gas-framework interactions (Lin et al., 2020). Such structural tuning strategies have been widely employed to enhance the separation selectivity of MOF membranes and continue to evolve toward more precise control of the local pore environment.

For example, ammonia-induced treatment can alter the local structure of ZIF-8 and promote a more rigid selective pathway (Choi et al., 2026; An et al., 2021), whereas defect-engineered UiO-66 provides an effective means of simultaneously tuning microporosity and mass transport (Lee et al., 2021). In addition, strategies such as varying linker length, regulating framework interactions, or introducing polymers directly into MOF pore windows, as in the polymer-in-cage approach, allow separation performance to be optimized for target gases while preserving the intrinsic framework structure (Kim et al., 2026). Thus, MOFs should be viewed not simply as porous fillers, but as a platform for designing pore environments tailored to specific gas pairs.

2.2 Functional group engineering

Another major advantage of MOFs is the ability to introduce diverse functional groups into the framework or linker. In particular, polar groups such as amino (-NH₂) and carboxyl (-COOH) functionalities are beneficial because they can enhance interactions with acidic gases such as CO₂ while simultaneously improving interfacial compatibility with polymer matrices. Ligand functionalization has therefore emerged as an important strategy for regulating both diffusion and sorption behavior, and amine functionalization is especially well known for improving CO₂ adsorption affinity and enhancing CO₂/CH₄ or CO₂/N₂ separation performance.

Representative studies using amino-functionalized ZIF-8-NH₂ and UiO-66-NH₂ have shown that hydrogen bonding and π-π interactions with the polymer matrix can suppress interfacial void formation and enable defect-free MMMs even at high filler loadings (Zhao et al., 2024; Chen et al., 2022). In addition, amino groups increase CO₂-philic interactions, leading to simultaneous improvements in CO₂ permeability and ideal selectivity. For example, in TEPA-functionalized MIL-101(Cr)/Pebax membranes, the grafted amine groups significantly enhanced CO₂/CH₄ separation performance by increasing affinity toward CO₂ (Khoshhal Salestan et al., 2021).

Meanwhile, COOH-functionalized MOFs are effective in promoting interfacial crosslinking with polymers (Xu et al., 2026). In UiO-66-COOH-based MMMs, thermal treatment induced a dual crosslinked network between the polymer and MOF, which enhanced the molecular sieving effect and substantially improved CO₂/N₂ ideal selectivity. These findings suggest that functional group engineering is not limited to enhancing gas affinity, but also offers an effective route to interfacial stabilization, defect suppression, and polymer chain packing control.

2.3 Hybrid MOF-based membranes with other materials

Although MOFs are promising on their own, their performance and structural stability can be further improved through hybridization with other materials such as graphene oxide (GO), ionic liquids (ILs), and polymers. Recent MOF membrane studies have highlighted integration with other species as an important development direction, since it combines the highly porous structure of MOFs with the mechanical robustness, processability, or selective interactions of other materials.

Among these, GO has emerged as a particularly effective additive for improving dispersion stability and interfacial compatibility in MOF-based membranes. In GO-modified MOF-74/Pebax membranes, GO nanosheets suppressed MOF aggregation and extended the gas diffusion pathway, resulting in markedly improved CO₂/N₂ ideal selectivity (Feng et al., 2024). Likewise, in GO-assisted assembly of CuBDC nanosheet membranes, GO effectively filled the voids between rigid MOF nanosheets, thereby enhancing membrane continuity and mechanical stability (Yang et al., 2019).

IL/MOF/polymer hybrid systems are also effective in constructing CO₂-philic transport pathways. In [EMIM][OAc]/CuBTC/Pebax membranes, incorporation of the IL/MOF composite improved both CO₂ permeability and CO₂/N₂ ideal selectivity, with some membranes even surpassing the Robeson upper bound (Habib et al., 2022).

In addition, crosslinking strategies between polymers and MOFs have been widely used to address interfacial defects and plasticization issues. In Mg-MOF-74/polymer of intrinsic microporosity (PIM-1) membranes, chemical crosslinking between the MOF surface and polymer chain ends generated an interconnected microporous network, while ionic cross-linked MOF/polymer MMMs effectively suppressed polymer chain mobility and interfacial voids (Tien-Binh et al., 2016; Jo et al., 2024). Collectively, these hybridization strategies combine the molecular sieving properties of MOFs with the interfacial stabilization capabilities of other materials, making them highly important for the development of high-performance MOF-based gas separation membranes.

3 Gas separation using MOF-based membranes

Owing to their highly tunable pore sizes, versatile chemical functionalities, and excellent compatibility with hybrid architectures, MOFs have emerged as one of the most promising classes of membrane materials for gas separation. In particular, the ability to precisely tailor sorption affinity and diffusion pathways through pore size engineering, functional group modification, and integration with complementary materials offers significant advantages for achieving high separation performance. As a result, MOF-based membranes have been extensively investigated for a wide range of gas separations, including H₂ purification, CO₂ separation, olefin/paraffin separation, and O₂/N₂ separation. Recent studies have demonstrated that the synergistic combination of molecular sieving, adsorption selectivity, and interfacial engineering can effectively overcome the conventional permeability-selectivity trade-off associated with polymeric membranes.

Before discussing the representative gas separation applications covered in this review, it should be noted that the MOF-based membrane architectures described herein differ fundamentally in membrane configuration, gas transport characteristics, performance metrics, fabrication strategies, and characteristic defect types. Accordingly, although the representative studies are organized according to target gas separations, the membrane architecture is explicitly identified whenever different membrane configurations are discussed to provide a clearer structural context. In addition, because the representative studies were conducted under different experimental conditions, including temperature, pressure, feed composition, membrane thickness, and testing mode, the reported performance values should not be interpreted as direct quantitative comparisons. Instead, they are intended to highlight representative advances in MOF-based membrane design for each target gas separation. To facilitate proper interpretation, the corresponding operating conditions for each study are summarized in Table 1.

TABLE 1. Summary of gas separation performance for the MOF membranes discussed in this review.

Permeance values are expressed in gas permeation units (GPU = 10⁻⁶cm³(STP)/cm²⋅sec⋅cmHg). Permeability values for dense, homogeneous membranes are enclosed in parentheses and expressed in Barrer (Barrer = 10⁻¹⁰cm³(STP)/cm⋅sec⋅cmHg). The mathematical relationship is defined by P = J × l, where l represents the selective layer thickness.

3.1 Hydrogen separation

Hydrogen separation represents one of the most important applications of MOF-based membranes because the extremely small kinetic diameter of H₂ enables efficient molecular sieving through sub-nanometer pores. Recent advances have shown that pore rigidification, stacking engineering, and interfacial stabilization are highly effective approaches for enhancing H₂ selectivity.

For example, an ammonia-treated ZIF-8 membrane generated locally rigidified selective pathways, achieving an H₂ permeance of 376 gas permeation unit (GPU) and an H₂/N₂ ideal selectivity of 122.4 (Choi et al., 2026). Similarly, a CuBDC-NO₂ nanosheet membrane exploited the controllable stacking behavior of MOF nanosheets to precisely regulate the effective aperture to 0.372 nm, resulting in an H₂ permeance of 1,326 GPU together with H₂/CO₂ and H₂/CH₄ selectivities of 266 and 536, respectively (Wu et al., 2024). These studies highlight the unique capability of MOFs to precisely tailor pore structures for highly selective H₂ sieving.

Hybridization strategies have also demonstrated remarkable effectiveness. A GO-assisted CuBDC nanosheet membrane utilized GO nanosheets to repair inter-nanosheet voids and construct a continuous selective layer, achieving an H₂ permeance of 2,867 GPU and an H₂/CO₂ separation factor of 95.1 (Yang et al., 2019). Likewise, a MOF-801@MXene membrane combined the intrinsic porosity of MOFs with the well-defined nanochannels of MXene, creating additional transport pathways for H₂ while suppressing CO₂ diffusion, thereby exhibiting an H₂ permeance of 2334 GPU and an H₂/CO₂ ideal selectivity of 29.4 (Li et al., 2022). Furthermore, a soft-solid Zn₂(Bim)₄/polyamide composite membrane synergistically integrated ordered MOF interlayer channels with the defect-healing effect of a polymer layer, delivering an exceptional H₂/CO₂ separation factor of 1084 (Shu et al., 2022). In this system, the straight interlayer galleries of Zn₂(Bim)₄ served as rapid H₂ transport pathways, whereas the polyamide layer effectively eliminated non-selective defects and maximized intrinsic molecular sieving performance.

Although Table 1 primarily summarizes representative supported MOF membranes for H₂ separation, MMMs have also demonstrated excellent separation performance through interfacial engineering. Interfacial engineering in mixed-matrix membranes (MMMs) has also emerged as an important strategy. A fluorinated FZIF-9/6FDA-TFMB MMM exploited the facile functionalization capability of MOFs by introducing -CF₃ groups, simultaneously optimizing pore size and MOF/polymer compatibility. Consequently, the membrane achieved an H₂ permeability of 159 Barrer and an H₂/CH₄ ideal selectivity of 295, approaching the 2015 Robeson upper bound (Yao et al., 2026). Returning to supported MOF membranes, a defect-rich MIL-125 Ti-MOF membrane prepared using titanium-oxo clusters utilized defect engineering to regulate adsorption and diffusion characteristics, yielding H₂/N₂ and H₂/CH₄ selectivities of 64.9 and 40.7, respectively (Wang et al., 2022). Collectively, these studies demonstrate that precise control of pore architecture and interfacial structure is essential for developing highly selective and highly permeable H₂ separation membranes.

3.2 Carbon dioxide separation

Carbon dioxide separation is the most extensively investigated application of MOF-based membranes because the intrinsic characteristics of MOFs, including CO₂-philic functionalities, open metal sites, and tunable microporous structures, are highly advantageous for selective CO₂ transport. Consequently, defect engineering, functional group modification, interfacial crosslinking, and hybridization with graphene oxide (GO) or ionic liquids (ILs) have been widely explored to improve CO₂ permeability and selectivity.

Defect engineering has proven particularly effective for creating rapid and selective CO₂ transport pathways. Defect-engineered UiO-66/poly (ethylene glycol) diacrylate (PEGDA) MMMs introduced additional microporosity and transport channels through framework defects, resulting in a CO₂ permeability of 470 Barrer and a CO₂/N₂ ideal selectivity of 41, corresponding to approximately a four-fold increase in permeability compared with the pristine PEGDA membrane (Lee et al., 2021). More recently, a polymer-in-cage strategy exploited the tunable pore windows of high-aspect-ratio NZIF-8 nanoplates to create tortuous diffusion pathways, achieving a CO₂ permeance of 333 GPU and a CO₂/N₂ ideal selectivity of 80 (Kim et al., 2026).

Functional group engineering has also been extensively employed to enhance CO₂ affinity and MOF/polymer compatibility. Incorporation of amino-functionalized ZIF-8-NH₂ into a carboxyl-containing polyimide matrix enabled strong hydrogen bonding and π–π interactions at the interface, allowing defect-free MMM fabrication even at a filler loading of 50 wt% and yielding a CO₂/CH₄ ideal selectivity of 89.4 (Zhao et al., 2024). Similarly, UiO-66-NH₂ incorporated into a Tröger’s base polyimide matrix simultaneously enhanced CO₂-philic interactions and disrupted polymer chain packing, increasing the CO₂ permeability to 415 Barrer while maintaining a CO₂/CH₄ ideal selectivity of 25.0 (Chen et al., 2022). In another example, TEPA-functionalized MIL-101(Cr)/Pebax membranes combined the high surface area of MOFs with the strong CO₂ affinity of amine groups, achieving a CO₂ permeability of 34.6 Barrer and a CO₂/CH₄ ideal selectivity of 46.3 (Khoshhal Salestan et al., 2021).

COOH-functionalized MOFs have demonstrated particular effectiveness in promoting interfacial crosslinking. In UiO-66-COOH-based MMMs, the MOF acted not only as a porous filler but also as a crosslinking platform, inducing the formation of a polymer-MOF dual-crosslinked network during thermal treatment. This structure yielded a CO₂/N₂ ideal selectivity of 61.9 together with enhanced anti-plasticization stability (Xu et al., 2026). Similarly, Mg-MOF-74/PIM-1 MMMs utilized chemical crosslinking between hydroxyl-functionalized MOFs and polymer chain ends to form interconnected microporous networks, increasing CO₂ permeability from 6500 to 21,000 Barrer while simultaneously improving CO₂/CH₄ ideal selectivity from 12.3 to 19.1 (Tien-Binh et al., 2016). Ionic cross-linked MIL-101(Cr)-based MMMs further demonstrated that MOF functionalization can effectively suppress polymer chain mobility and interfacial defects, resulting in a CO₂ permeability of 1981 Barrer (Jo et al., 2024).

Hybridization with other materials has also substantially improved CO₂ separation performance. GO-modified MOF-74/Pebax MMMs combined the strong CO₂ affinity of MOFs with the diffusion barrier effect of GO nanosheets, achieving a CO₂/N₂ ideal selectivity of 76.96, representing an approximately 197% increase compared with pristine Pebax membranes (Feng et al., 2024). IL/MOF/polymer hybrid membranes have likewise shown exceptional performance. For example, an [EMIM][OAc]/CuBTC/Pebax MMM exploited both the intrinsic porosity of MOFs and the high CO₂ solubility of ionic liquids, delivering a CO₂ permeability of 335 Barrer and a CO₂/N₂ selectivity of 176 (Habib et al., 2022). An IL-modified MOF-177/Pebax MMM further achieved a remarkably high CO₂/N₂ ideal selectivity of 622 with a CO₂ permeability of 137 Barrer (Habib et al., 2024). Additionally, an amino-functionalized ZIF-8-based MOF-protruding thin-film MMM utilized strong interfacial interactions and high-aspect-ratio fillers to achieve a CO₂ permeance of 778 GPU and a CO₂/CH₄ separation factor of 34 while significantly improving resistance to plasticization and physical aging (Song et al., 2023).

Although Table 1 focuses primarily on representative MMMs for CO₂ separation, other membrane architectures have also shown promising performance. In particular, MOF-derived glass membranes have recently attracted considerable attention because they eliminate crystalline grain boundaries while maintain continuous gas transport pathways. As a representative MOF-derived glass membrane, a MIL-101/a_gZn-P-dmbIm crystal-glass composite membrane combined the high porosity of MOFs with the excellent processability of glass matrices, achieving a CO₂ permeability of 19,157 Barrer and a CO₂/N₂ ideal selectivity of 61.9 under mixed-gas conditions (Li et al., 2025a). Likewise, a topology-engineered ZIF-derived MOF glass membrane partially preserved the pore topology of the crystalline precursor after vitrification, delivering a CO₂ permeance of 37,000 GPU and a CO₂/N₂ separation factor of 14.8 (Li et al., 2025b). These results clearly demonstrate that the structural diversity and design flexibility of MOFs provide powerful opportunities for the development of next-generation CO₂ separation membranes.

3.3 Other gas separations

Beyond H₂ and CO₂ separation, MOF-based membranes have demonstrated significant potential for challenging gas separations such as olefin/paraffin and O₂/N₂ separations. Because these gas pairs possess very similar molecular sizes and physicochemical properties, precise pore aperture control, adsorption selectivity, and filler-polymer interfacial engineering become particularly important. The structural tunability and functionalization capability of MOFs make them especially attractive for these demanding separations.

For olefin/paraffin separation, defect-engineered AZIF-8 nanoparticles enhanced framework rigidity and molecular sieving precision while simultaneously improving compatibility with polymer matrices. As a result, 6FDA-DAM/AZIF-8 MMMs achieved a C₃H₆ permeability of 79.4 Barrer and a C₃H₆/C₃H₈ ideal selectivity of 39.8 (An et al., 2021). In addition to the MMMs summarized in Table 1, supported MOF membranes have also demonstrated excellent separation performance. Furthermore, layered MOF membranes modified with an ionic liquid/AgBF₄ composite combined the uniform pore structure of MOFs with Ag⁺-mediated facilitated transport, effectively transforming an intrinsically non-selective membrane into an olefin-selective membrane. Consequently, mixed-gas separation factors of 28.8 for C₃H₆/C₃H₈ and 12.0 for C₂H₄/C₂H₆ were obtained (Yang et al., 2021).

Gallate-based MOFs have also emerged as promising fillers for olefin/paraffin separations. A Ni-gallate/6FDA-DAM MMM utilized moderately confined pores and high ethylene affinity to simultaneously enhance C₂H₄ permeability and C₂H₄/C₂H₆ ideal selectivity beyond the polymer upper bound (Chen et al., 2021). More recently, a Co-gallate/PIM-1 MMM featuring a three-dimensionally interconnected porous framework achieved a C₃H₆ permeability of 3552 Barrer and a C₃H₆/C₃H₈ ideal selectivity of 8.8, corresponding to improvements of 106.5% and 131.6%, respectively, compared with pristine PIM-1 (Wang et al., 2025).

MOF-based membranes have also shown promising performance for air separation. An o-carborane-modified ZIF-8/PIM-1 MMM combined molecular sieving with preferential N₂ adsorption inhibition, thereby enhancing O₂ diffusion selectivity. The optimized membrane achieved an O₂ permeability of 796.5 Barrer and an O₂/N₂ separation factor of 8.9, surpassing the 2015 Robeson upper bound (Qin et al., 2024). Overall, these studies demonstrate that MOF-based membranes constitute a highly versatile platform capable of addressing a broad spectrum of industrially important gas separations through precise pore engineering, functionalization, and hybridization strategies.

4 Conclusion

MOF-based membranes have developed into one of the most promising platforms for next-generation gas separations because their crystalline and modular structures allow unprecedented control over pore size, pore chemistry, and membrane architecture. As summarized in this review, fine-tuning of pore size, incorporation of functional groups such as amino and carboxyl groups, and hybridization with materials such as GO, ionic liquids, and polymers have all been shown to effectively enhance molecular sieving, interfacial compatibility, and transport selectivity. These strategies have enabled strong performance in hydrogen separation, carbon dioxide capture, and other difficult separations such as olefin/paraffin and O₂/N₂ systems. At the same time, the practical deployment of MOF membranes will require continued progress in scalable synthesis, defect control, and long-term stability. For pure MOF films, membrane substrate bonding, grain-boundary defects, and mechanical robustness remain major challenges. For MMMs, filler agglomeration, interfacial voids, plasticization, and physical aging continue to limit performance, especially under mixed-gas and high-pressure conditions. Therefore, future progress will likely depend on developing more robust interface-engineering strategies, more scalable fabrication routes, and more realistic testing protocols that better reflect industrial operating environments. Overall, the structural diversity and chemical tunability of MOFs provide a strong foundation for the continued development of high-performance gas separation membranes. With further advances in materials design and process integration, MOF-based membranes are expected to play an increasingly important role in energy-efficient and environmentally relevant separations.

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Footnotes

Edited by: Arash Mollahosseini, National Institute for Nanotechnology (NRC-CNRC), Canada

Reviewed by: Mao Fu, Guizhou Normal University, China